Please help me!

Question

A police car sounding a siren with a frequency of 1280 Hz is traveling at 110.0 km/hr. (Express your answer using 4 significant figures.)

 

a) What frequency does an observer standing next to the road hear as the car approaches?

 

b) What frequency does an observer standing next to the road hear as the car recedes?

c) What frequency is heard in a car traveling at 110.0 km/hr. in the opposite direction to the police car before passing the police car? 

d) What frequency is heard in a car traveling at 110.0 km/hr. in the opposite direction to the police car after passing the police car? 

e) The police car passes a car travelling in the same direction at 90.00 km/hr. What frequency is heard in the car before being overtaken by the police car?

f) The police car passes a car traveling in the same direction at 90.00 km/hr. What frequency is heard in the car after being overtaken by the police car?

Answer 1

There is an equation associated with the Doppler effect which explains sound frequencies by observer which goes: f = fo ((V +/- Vo)/(V -/+ Vs)). f is the observed frequency, fo is the true frequency, V is the velocity of the sound waves, Vo is the observer's velocity, and Vs is the velocity of the source. For the components of the equation, (V + Vo) is when observer is approaching the source, (V - Vo) is when the observer is leaving, (V - Vs) is when the source approaches the observer, and (V + Vs) is when the source leaves the observer. Vo or Vs = 0 if the observer or source isn't moving. The V (speed of sound) is 1235 km/h.

a. Here the equation is f = 1280 ((1235)/(1235-110.0)) which is solved for f = 1405 hz

b. Here it would be f = 1280 ((1235)/(1235+110.0)), so f = 1175 hz

c. Now the source and observer approach each other, so it's f = 1280 ((1235 + 110.0)/(1235 - 110.0)) so f = 1530 hz

d. Now the source and observer leave each other, f = 1280 ((1235 - 110.0)/(1235 + 110.0)) = 1071 hz

e. The observer is leaving a source that's approaching, so f = 1280 ((1235 - 90.00)/(1235 - 110.0)) = 1303 hz

f. Now the observer is approaching and the source is leaving. f = 1280 ((1235 + 90.00)/(1235 + 110.0)) = 1261 hz